The update updated, 2014-04-28: unbricking is fairly easy, see http://valentijn.sessink.nl/?p=517
Please note that I received some reports from people that tried to flash their RK3066 stuff – but it would not boot afterwards. And in fact, that’s what I experienced when I tried to flash my Minix Neo X5.
Using the procedure as described here, all seemed to work well: I could read the flash memory, dump it to a file, mount the file, replace some stuff, write it back, but then – nothing.
Re-reading the file that I just wrote gave me a different file. So in fact, there might be something in the newer RK3066 firmware that prevents rkflashtool from working. It seems to work – but it does not.
Reading the same blocks of memory always gave me the same results (and the first time, the block seemed a correct Linux filesystem), so I don’t think the problem is in the reading. Writing back the flash memory however was problematic: writing a block and reading it back would not give me the same information. Unfortunately, I don’t have the time to find out what’s wrong – I don’t own Windows machines and subsequently gave away my X5 to a RK3066-Linux-developer (that was never heard of afterwards, but that’s another story).
Luckily for some, there’s always the original RK3066 firmware flasher: from within Windows, you can easily flash a firmware – even if you completely bricked your tablet. But for those working with free software, the possibilities are fewer: you might need to turn to a friend who does run Windows to unbrick your RK3066.